The present invention relates to a telephonic alphanumeric data transmission system, and, more particularly, to a system for providing transmission of alphanumeric data through the standard switched network telephone system utilizing a standard telephone set.
There is an ever increasing need to provide direct access to computer based systems without the necessity of special transmitters. For example, it is becoming increasingly desirable to conduct business transactions by phone without requiring human intervention between the caller and data processing apparatus. Specific examples include credit card validation, banking, off track betting, stock market transactions, commodities transactions, placing reservations, ticketing, and retail and wholesale sales.
It would be desirable to transmit data utilizing the Touch Tone (DTMF) transmitter of the standard telephone set. However, a problem arises in that the standard telephone dial or touch tone key pad is designed to provide only 10 or 12 distinct characters, necessitating the interposition some manner of translating device between the standard telephone set and the computer in order to transmit alphanumeric data.
A typical Touch Tone telephone set (transmitter) typically includes 12 push-buttons, or keys, disposed in a matrix of 4 horizontal rows by 3 vertical columns. Each of the keys has associated therewith 2 distinct frequencies: a frequency chosen from a group ("A") of relatively low frequencies, corresponding to the row wherein the button is disposed; and a frequency selected from a group ("B") of relatively high frequencies, corresponding to the column wherein the button is disposed. Depression of a given key causes transmission of a dual tone (DTMF) signal having frequencies components at both the group A (row) and group B (column) frequencies associated with the disposition of the key in the matrix.
Each key of the Touch Tone phone conventionally is inscribed with both numerical designations (0-9) as well as alphabetic designations, as shown in Table I.
TABLE I ______________________________________ Alphabetic Numeric Div. 1 Div. 2 Div. 3 ______________________________________ 1 -- -- -- 2 A B C 3 D E F 4 G H I 5 J K L 6 M N O 7 P R S 8 T U V 9 W X Y * -- -- -- 0 -- -- -- # -- -- -- ______________________________________
The alphabetic characters "Z" and "Q" are not portrayed on the standard touch tone set, but can be considered to be associated with a predetermined one of the numeric 0 or 1 keys. The individual keys will hereinafter be referred to by the numeric or * or # symbols inscribed thereon.
In general, systems for translating touch tone signals into alphanumeric data are known. For example, U.S. Pat. No. 3,381,275 issued on Apr. 30, 1968 to the present inventor, describes a translator system utilizing what is known as a "twin depression" translation technique. Simultaneous depression of a plurality of keys produces a signal having frequency characteristics (e.g., a single frequency), which may be discriminated from the pairs of frequencies generated in response to depression of a single key. For example, an alphabetic character may be transmitted using the "twin depression" as follows. The alpha characters, i.e., alphabetic characters, may be considered to be divided into three divisions, (hereinafter referred to as "placement divisions" or "order divisions") corresponding to the order or placement in which the characters are inscribed on the key:
Division 1-A, D, G, J, M, P, T, W; PA1 Division 2-B, E, H, K, N, R, U, X, (Z); PA1 Division 3-C, F, I, L, O, S, V, Y, (Q).
An alphabetic character is transmitted by first simultaneously depressing a predetermined pair of keys indicative of the placement division of the character (e.g. simultaneously depressing keys 2 and 3 for alphabetic characters in Division 1; 5 and 6 for alphabetic characters in Division 2; and 8 and 9 for alphabetic characters in Division 3. The key inscribed with the particular alphabetic character is then depressed. A return to the numeric mode can be effected by depressing a designated clear key (e.g., *), whereafter depression of a key will be translated into its numeric designation.
Another example, of a touch tone to alphanumeric translator is described in U.S. Pat. No. 3,618,038 issued Nov. 2, 1971 to Edward S. Stein. The Stein translator utilizes what is known as the "delayed depression" translation technique, wherein depression of keys having different durations are discriminated. For example, an alphabetic character is represented by first depressing a key indicative of the placement division of the alphabetic character (e.g. the 1 key for Division 1, the 2 key for Division 2, or the 3 key for Division 3) for a duration longer than a preset limit, e.g. 290 milliseconds. The key inscribed with the particular alphabetic character is thereafter depressed for a duration less than the preset limit. Return to the numeric mode is effected by depressing a fourth symbol (e.g. the 0 key) for a period greater than the preset limit.
Another touch tone to alphanumeric translation technique has been proposed whereby an alphabetic mode is entered by depressing a first key (e.g., *), followed by depressing a designated key corresponding to the placement division of a particular alphabetic character (e.g., 1, 2, or 3), followed by depression of the key on which the alphabetic character is inscribed.
In addition, other translation techniques whereby each alphanumeric symbol is represented by a specific sequence of DTMF signals, with each character separated by a specific designated DTMF signal (e.g. #) have been proposed. An example of such a translation technique is described in Broomfield et al, Electronics, "Making a Data Terminal Out of the Touch-Tone Telephone", McGraw Hill, July 3, 1980.
Each of the above translation systems may have advantages in respect of the transmission of certain types of data. However, such techniques are, in general, slow and cumbersome, in that different combinations of a plurality of keys must be depressed to transmit the alphabetic characters. Many people do not possess sufficient manual dexterity to use such systems proficiently.
In addition, a further problem is inherent in the prior art translation systems, in that the user is provided no feedback during the entry of the data. The user is provided no indication that any valid data character has been transmitted, much less an indication of the specific data character transmitted. Particularly in view of the multi-key entry techniques, mistakes in the data often occur.